Color and lightness qualities of digital images
The following terminology is helpful to know when learning about the types of digital images:
n Tonal range (or dynamic range). This term refers to the range of dark to light values in
an image, usually referred to as shadows, midtones, and highlights. An image that contains
all or most of the possible tones, rather than a smaller portion of the possible tones,
usually appears more detailed and is said to have a large tonal range, or dynamic range.
Tones also may be referred to as levels or intensities.
n Brightness, lightness, luminosity, luminance. These terms refer to dark to light tonal
characteristics, as opposed to color characteristics. They can be thought of as describing
the image as if the colors had been converted to blacks, grays, and whites.
n Hue. Hue is identified by the name of the color, such as red, orange, or green. The lightness
or darkness of a color is thought of as separate from the hue. Hue can be measured
on a location on the standard color wheel and expressed as a degree between 0° and 360°.
n Color. In many instances in Photoshop, color refers to the hue, as a separate quality from
dark to light tonal qualities. For example, it is common to say, “The color in this image is
good and needs to stay the same, but I need to make changes to the luminosity.”
But sometimes color refers to the overall qualities of a color — the hue component
together with the lighter or darker components of the color. For example, it is just as correct
to say, “I will use a darker blue color fo the type,” as it is to say, “I will use the same
blue color but one that has a darker luminosity for the type.”
n Saturation. The strength or purity of the color, or chroma, saturation represents the
amount of hue in the color compared to the amount of black, gray, or white in the color. If
a color contains some black or gray, it may look darker, and/or muted; if iti contains some
white, it may look lighter, muted, and/or pastel. The maximum amount of hue, with no
black, gray, or white mixed in, would be fully saturated and look like pure vivid color.
                                                           Figure 1.1